Certain ferrous alloys including INCOLOY.RTM. alloy 825 or UNS alloy NO8825 (hereinafter referred to as "alloy 825") are particularly useful for their exceptional resistance to many corrosive environments. INCOLOY.RTM. is a trademark of Inco International, Inc. These alloys include nickel, iron, and chromium with additives of molybdenum, copper, and titanium. A typical composition of INCOLOY.RTM. alloy 825 by weight percent is provided in Table 1.
TABLE 1 ______________________________________ ALLOY 825 COMPOSITION (WT %) ______________________________________ Aluminum 0.2 max. Carbon 0.05 max. Chromium 19.5-23.5 Copper 1.5-3.0 Iron Balance Manganese 1.0 max. Molybdenum 2.5-3.5 Nickel 38.0-46.0 Phosphorus 0.03 max. Silicon 0.5 max. Sulfur 0.03 max. Titanium 0.6-1.2 ______________________________________
The nickel content of alloy 825 provides resistance to chloride-ion stress-corrosion cracking. The nickel, in combination with the molybdenum and copper, also gives outstanding resistance to reducing environments such as those containing sulphuric acid or phosphoric acid. The molybdenum provides resistance to pitting and crevice corrosion. The alloy's chromium content confers resistance to a variety of oxidizing substances such as nitric acid, nitrate, and oxidizing salts. The titanium addition serves, with an appropriate heat treatment, to stabilize the alloy against sensitization to interrangular corrosion.
The resistance of alloy 825 to general and localized corrosion under diverse conditions gives the alloy broad usefulness. Alloy 825 is used in chemical processing, pollution control, oil and gas recovery, acid production, pickling operations, nuclear fuel reprocessing, and handling of radioactive wastes.
In order to deoxidize melts of alloy 825, calcium in amounts of 0.001 to less than 0.003 weight percent and about 0.15 percent aluminum have been added to the alloy during an argon oxygen decarburization (AOD) process. Unfortunately, ingots produced with this deoxidation process lack sufficient high temperature ductility for hot rolling various product configurations. Therefore, it has been necessary to use electroslag remelting (ESR) of each ingot to increase the hot workability to sufficient levels for slab conditioning and finishing operations. The additional step of ESR adds significantly to the processing costs of the finished product.
Accordingly, a need remains for an alloy having the corrosion resistance, mechanical properties, and weldability of alloy 825 with enhanced hot ductility which does not require ESR before hot working of the alloy.